1. Field of the Invention
The present invention relates to acoustic touchscreens, in particular acoustic touchscreens having narrow reflective arrays and increased touch-sensitive areas.
2. Description of Related Art
An acoustic touchscreen has a touch-sensitive area on which the occurrence and location of a touch is sensed via the touch""s effect on the transmission of acoustic waves thereacross. A common type of acoustic touchscreen employs Rayleigh waves (a term which, as used herein, subsumes quasi-Rayleigh waves). Illustrative disclosures relating to Rayleigh wave touchscreens include U.S. Pat. No. 4,642,423 (1987); U.S. Pat. No. 4,645,870 (1987); U.S. Pat. No. 4,700,176 (1987); U.S. Pat. No. 4,746,914 (1988); U.S. Pat. No. 4,791,416 (1988); Re 33,151 (1990); U.S. Pat. No. 4,825,212 (1989); U.S. Pat. No. 4,859,996 (1989); U.S. Pat. No. 4,880,665 (1989); U.S. Pat. No. 4,644,100 (1987); U.S. Pat. No. 5,739,479 (1998); U.S. Pat. No. 5,708,461 (1998) and U.S. Pat. No. 5,854,450 (1998). Acoustic touchscreens employing other types of acoustic waves such as Lamb or shear waves, or combinations of different types acoustic waves (including combinations involving Rayleigh waves) are also known, illustrative disclosures including U.S. Pat. No. 5,591,945 (1997) U.S. Pat. No. 5,854,450 (1998); U.S. Pat. No. 5,072,427 (1991); U.S. Pat. No. 5,162,618 (1992); U.S. Pat. No. 5,177,327 (1993); U.S. Pat. No. 5,243,148 (1993); U.S. Pat. No. 5,329,070 (1994); U.S. Pat. No. 5,573,077; and U.S. Pat. No. 5,260,521 (1993). The documents cited in this paragraph are incorporated herein by reference.
FIG. 1 illustrates the operation of a conventional acoustic touchscreen 1, having an active, or touch-sensitive area 2. A first transmitting transducer 3a is positioned outside of touch-sensitive area 2 and acoustically coupled to the surface of touchscreen 1. The transducer 3a sends an acoustic signal in the form of an acoustic wave 11 a traveling parallel to the top edge of touchscreen 1 and generally in the plane of touchscreen 1. Aligned in the transmission path of acoustic wave 11a is a first linear array 13 of partially acoustically reflective elements 4, each of which partially reflects (by approximately 90xc2x0) and partially transmits the acoustic signals, creating a plurality of acoustic waves (exemplary 5a, 5b, and 5c) traveling vertically (parallel to the Y-axis) across touch-sensitive area 2. (The spacing of reflective elements 4 is variable to compensate for the attenuation of the acoustic signals with increasing distance from first transmitter 3a.) Acoustic waves 5a, 5b, and 5c, upon reaching the lower edge of touchscreen 1, are again reflected by approximately 90xc2x0 (arrow 11b) by a second linear array 13 of partially acoustically reflective elements 4 towards a first receiving transducer 6a, where they are detected and converted to electrical signals for data processing. Along the left and right edges of touchscreen 1 are located a similar arrangement. A second transmitting transducer 3b generates an acoustic wave 12a along the left edge, and a third linear array 13 of partially acoustically reflective elements 4 creates therefrom a plurality of acoustic waves (exemplary 7a, 7b, and 7c) traveling horizontally (parallel to the X-axis) across touch-sensitive area 2. Acoustic waves 7a, 7b, and 7c are redirected (arrow 12b) by a fourth linear array 13 of partially acoustically reflective elements 4 towards receiving transducer 6b, where they are also detected and converted to electrical signals.
If touch-sensitive area 2 is touched at position 8 by an object such as a finger or a stylus, some of the energy of the acoustic waves 5b and 7a is absorbed by the touching object. The resulting attenuation is detected by receiving transducers 6a and 6b as a perturbation in the acoustic signal. A time delay analysis of the data with the aid of a microprocessor (not shown) allows determination of the coordinates of position 8.
Those skilled in the art will appreciate that it is not essential to have two sets of transmitting/receiving transducers to make a touchscreen. The device of FIG. 1, without one set of transducers, will still function as a touchscreen, detecting the occurrence of a touch and providing limited location information (one of the coordinates). Or, a touchscreen can be designed with only two transducers by using a common transmit/receive transducer scheme, as disclosed in FIG. 8 of U.S. Pat. No. 4,746,914.
In normal usage, a housing 9 (outline indicated by a dotted line in FIG. 1), typically made of molded polymer or sheet metal, is associated with touchscreen 1. Housing 9 contains a bezel 10 (outline also indicated by a dotted line in FIG. 1) that overlays touchscreen 1, concealing the transmitting and receiving transducers, the reflective elements, and other components, but exposing touch-sensitive area 2. This arrangement protects the concealed components from contamination and/or damage, presents a more aesthetically pleasing appearance, and defines the touch-sensitive area for the user.
A touchscreen may comprise a separate faceplate (typically made of glass, but other hard substrates may be used) overlaid on a display panel such as a cathode ray tube (CRT), a liquid crystal display (LCD), plasma, electroluminescent, or other type of display. Alternatively, it has been proposed to convert the CRT into a touchscreen by coupling the touchscreen components directly to the glass surface of the CRT, so that the CRT surface is the touch-sensitive surface. U.S. Pat. No. 4,746,914 discloses such a construction. A direct-on-CRT touchscreen construction is desirable because it eliminates a piece of glass or other material between the viewer and the CRT, increasing the perceived display brightness. Also, there are economic advantages in dispensing with the overlay glass and not having to modify CRT chassis to make room for the overlay glass.
Returning to FIG. 1, it is seen that the touch-sensitive area 2 is surrounded by border regions 15 (only two labeled), where the reflective elements 4 and the transmitting and receiving transducers 3a, 3b, 6a, and 6b are located. Reducing the width of border regions 15 increases the percentage of the frontal area of the device that may be allocated to touch-sensitive area 2. The touchscreen may also be more easily integrated and sealed with the monitor. Also, a touchscreen having narrower border regions 15 conveys the impression of a less cumbersome, sleeker design, making the product more attractive to a customer.
Further, where a touchscreen is constructed directly on the faceplate glass of a CRT, the touchscreen manufacturer may not have control over the width of border regions 15. A touchscreen manufacturer normally does not manufacture the CRT itself. Rather, the manufacturer works with the CRT as supplied by a monitor manufacturer (or, in the case of a monitor integrated with a computer CPU chassis, such as the iMac(trademark) computer from Apple Computer, from the computer manufacturer) and must adapt to whatever border region is provided. With some CRT""s, the provided border regions may be wide; with others, they may be narrow.
For the foregoing reasons, it is desirable to have the capability of making touchscreens compatible with narrower border regions 15. The key to reducing their width lies with reducing the width of arrays 13 and the transducers. However, the widths of these components are not reducible at will. The width of the array 13 is closely related to the beam width of the acoustic wave 11a, in that the deflected acoustic waves 5a, 5b, and 5c must contain sufficient acoustic energy for touch sensing purposes. If the array 13 is too narrow, only a small fraction of the acoustic wave 11a is intercepted, causing the deflected signals to be undesirably weak. Similar considerations apply with respect to the other reflector arrays. As for the transducers, a narrow transmitting transducer is undesirable because it causes the acoustic wave 11a to diffuse, due to diffractive effects. The physics of this wave mechanical effect corresponds to that of a wave passing through a narrow opening. Mathematical analysis of these wave mechanics effects are quite consistent with the observation that the width of the array 13 is also related to the size of the touch screen 1. The larger the touch screen, the wider the array 13 must be to capture enough of the acoustic signal downstream from the transducer to reflect enough signal across the touch sensitive area 2 for touch sensing purposes. Conventional touch screens have had array widths, in units of wavelengths of the acoustic signal, on the order of greater than ⅓ the square root of the array length, also in units of wavelength.
Thus, it is desirable to provide a new design for acoustic touchscreens capable of accommodating a narrower border region, via a design capable of employing narrower reflective arrays and/or narrower transducers.